1. Field of the Invention
Embodiments disclosed herein relate generally to a method for extracting hydrocarbons from drill cuttings. More specifically, embodiments disclosed herein relate to a method for extracting hydrocarbons from drill cuttings using liquid carbon dioxide. Most specifically still, embodiments disclosed herein relate to a method for extracting hydrocarbons from drill cuttings using liquid carbon dioxide at relatively low temperatures and pressures.
2. Background Art
In the drilling of wells, a drill bit is used to dig many thousands of feet into the earth's crust. Oil rigs typically employ a derrick that extends above the well drilling platform. The derrick supports joint after joint of drill pipe connected end to end during the drilling operation. As the drill bit is pushed further into the earth, additional pipe joints are added to the ever lengthening “string” or “drill string”. Therefore, the drill string includes a plurality of joints of pipe.
Fluid “drilling mud” is pumped from the well drilling platform, through the drill string, and to a drill bit supported at the lower or distal end of the drill string. The drilling mud lubricates the drill bit and carries away well cuttings generated by the drill bit as it digs deeper. The cuttings are carried in a return flow stream of drilling mud through the well annulus and back to the well drilling platform at the earth's surface. When the drilling mud reaches the platform, it is contaminated with small pieces of shale and rock that are known in the industry as well cuttings or drill cuttings. Once the drill cuttings, drilling mud, and other waste reach the platform, a “shale shaker” is typically used to remove the drilling mud from the drill cuttings so that the drilling mud may be reused. The remaining drill cuttings, waste, and residual drilling mud are then transferred to a holding trough for disposal. In some situations, for example with specific types of drilling mud, the drilling mud may not be reused and it must be disposed. Typically, the non-recycled drilling mud is disposed of separate from the drill cuttings and other waste by transporting the drilling mud via a vessel to a disposal site.
The disposal of the drill cuttings and drilling mud is a complex environmental problem. Drill cuttings contain not only the residual drilling mud product that would contaminate the surrounding environment, but may also contain oil and other waste that is particularly hazardous to the environment, especially when drilling in a marine environment.
In addition to shakers, various methods for removing hydrocarbons and contaminants from drill cuttings and drilling fluids have been employed. However, the high costs and plant construction complexity, significant energy waste, limited safety, especially when operating off-shore, and low efficiency have rendered such methods disadvantageous for extraction of hydrocarbons from drill cuttings.
Accordingly, there exists a continuing need for methods and systems for extracting hydrocarbons from drill cuttings.